It is well known that vitamin D is critical for good health — but can the sunshine vitamin protect against type 1 diabetes (T1D)? Current studies are attempting to answer this question.
Connecting the dots
Vitamin D is most well-known for its role in regulating bone metabolism. However, there has been increasing speculation about whether vitamin D levels are associated with T1D due to the presence of vitamin D receptors on insulin-secreting pancreatic beta cells and immune cells, as well as the influence of vitamin D on the immune system, including autoimmunity.
In the body, vitamins D2 and D3 are converted into a metabolite called calcidiol, which in turn is metabolized to calcitriol. Calcitriol helps suppress autoimmunity (in which the immune system attacks itself because it is unable to differentiate between invading foreign substances and its own cells and tissues). T1D may be partially attributed to destruction of the islet beta cells by the immune system, prompting the hypothesis that vitamin D might help prevent and manage T1D by regulating this autoimmune response.
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Genes, T1D and vitamin D
So, does this mean vitamin D supplementation is one answer to the question of how to prevent T1D? It isn’t quite that simple. Your genetic makeup could be an indicator as to whether vitamin D supplements will protect against T1D. The association between vitamin D and T1D is influenced by genes for the vitamin D receptor, vitamin D binding protein, and enzymes involved in vitamin D metabolism. Responsiveness to vitamin D supplements may vary depending on which genes are present in your DNA.
What does the research say?
Multiple studies have shown that vitamin D supplementation during early childhood can reduce the risk of T1D. Additionally, a Norwegian study showed that a high concentration of vitamin D during the last trimester of pregnancy reduced the risk of T1D in offspring.
Dr. Camillo Ricordi, director of the Diabetes Research Institute at the University of Miami, says, “Based on data from Grassroots Health (a U.S.-based non-profit public health research organization), there is significant evidence that there is a much lower incidence of T1D when 4000 IU/day is given to infants.”
However, these results are inconsistent. In a Finnish study, the status of vitamin D during the first trimester of pregnancy appeared to have no association with the risk of T1D in offspring. Additionally, according to a Finnish study in newborns, vitamin D concentrations at birth were not associated with the development of T1D later in life.
These inconsistent findings may be attributed to the role played by vitamin D metabolism genes in the development of islet autoimmunity and T1D. For example, a study conducted in Norway showed that higher blood levels of vitamin D at birth was associated with a lower risk in children with a specific genetic makeup.
What does this mean for people with T1D?
Dr. Ricordi says, “It would most likely have a better impact if supplementation is done [preventively]. However, even if the subjects have been already diagnosed with diabetes, vitamin D supplementation could be of assistance to make the subjects healthier in general, preventing the development of other chronic disease conditions.”
Dr. Ricordi is part of a team that is conducting a clinical trial called POSEIDON, which is evaluating vitamin D in combination with omega-3 fatty acids in T1D. “Our current randomized prospective trial will determine whether vitamin D3 supplementation alone or a combination of vitamin D3 and omega-3 will have an impact on disease progression, residual insulin production and metabolic control. Our initial observations have been encouraging in this direction, indicating that early intervention following T1D diagnosis with high-dose omega-3 and vitamin D3 can halt progression and possibly reverse autoimmunity, if the ratio of arachidonic acid/eicosapentaenoic acid (surrogate markers of omega-6/omega-3) is between 1.5 and 3, and serum levels of vitamin D are greater than 40 ng/ml,” reveals Dr. Ricordi.
Since the relationship between vitamin D and T1D is complicated by various factors, it is important to conduct long-term studies with different doses and dosing schedules, taking into consideration multiple factors, such as specific populations of people with the condition and individual genetic responsiveness to vitamin D.
One such study is the international TEDDY clinical study, which aims to identify factors that trigger T1D in predisposed people and those that protect against the condition, including the effect of vitamin D supplements. This trial was started in 2004 and is expected to be completed in 2025. Recent results suggest that vitamin D levels in childhood play a protective role against islet autoimmunity.
Another challenge of vitamin D research is that results vary considerably across studies. According to Dr. Ricordi, improper study design and analysis will lead to inconsistent results across studies; for example, analysis based only on the dose of supplementation might lead to false conclusions. “There will likely be no difference if the serum [blood] levels of the treated individuals are already above 40 ng/ml range. A benefit can be shown primarily for subjects with baseline levels less than 30 ng/ml.” He therefore advises that studies should consider the baseline levels of vitamin D when deciding on the dose of supplementation.
Hope for the future
If current and future studies can confirm a protective role of vitamin D in T1D, it will have huge benefits for both predisposed people and those with T1D, particularly through supplementation and routine monitoring of vitamin D levels.